Orbiting space junk heightens risk of satellite catastrophes

Earlier this month, two satellites crashed into one another over Siberia. This …

Earlier this year, an aging, defunct Russian Space Forces satellite, Kosmos 2251, collided over Siberia with the US-based Iridium Satellite, LLC's Iridium 33. The collision happened around noon Eastern time on February 11th. It destroyed the two satellites and left a new cloud of space debris in an already overcrowded orbital neighborhood. This area is already thoroughly littered, thanks, in part, to China's decision to target one of its own weather satellites with an anti-satellite weapon. Within a day of the collision, the US space tracking systems had identified hundreds of individual pieces of debris.

When the two satellites collided, they were each traveling at a speed of around 17,000mph relative to the Earth, and nearly 22,000mph relative to one another. The collision occurred over northern Siberia (72.52 oN, 97.39 oE) at an altitude of 490 miles. Given the limitations of the US space tracking system—it can only reliably track debris particles greater than 5 to 10cm (2 to 4 inches)—it is hard to know exactly how much debris this collision has generated. To date, there have been 352 items identified as coming from this collision.

Had the two hit head-on, instead of at an obtuse (102.2o) angle, models developed at NASA calculate that there would have been more than 62,000 pieces of debris greater than 1cm in diameter. Despite this small size, the extreme orbital velocities mean that 1cm debris can significantly damage an orbiting satellite. While the collision poses no immediate concern to astronauts in the International Space Station—it is far below where the collision occurred—Chinese scientists have expressed concern that the debris field could damage some of their country's satellites, specifically the ones in Sun-synchronous orbits.

This event creates a unique opportunity to look at the real dangers satellites face on a daily basis. In a blog post over at ArmsControlWonk,
Dr. Jeffrey Lewis highlights some of those. Right
now, according to the Union
of Concerned Scientists'Satellite
Database, there are 441 satellites, both operational and
non-operational, in Low Earth Orbit (LEO means altitudes less than 1200km). And satellites represent only a small fraction of the debris greater than a
few centimeters that is orbiting the planet. In order to calculate
the danger a given satellite faces, one needs to know how much junk
could potentially be in the orbit of the craft.

The simplest way to address this problem is to assume a constant or average flux around the entire planet, e.g. that there are N objects per volume of space per unit time. The problem is that reality isn't that simple, as the amount of debris is highly dependent on the altitude. At the equator, the debris flux has two strong peaks around 800 and 1500km high, with little material in between.

The other complication arises from the manner in which we, humanity, put stuff into space. A not-so-insignificant number of the satellites are put into near-polar orbits—that is, they travel around the planet going from the North pole region to the South, or vice-versa. This creates a sort of traffic jam of satellites at the Earth's poles; since a large number of craft are passing over this small region of space, the chances for a collision go up dramatically. According to NASA calculations, there is 10 times more debris per cubic kilometer in the high latitude regions (�75�) than there is at the equator (0�).

Like many other satellites in the sky, Iridium-33 was in a near-polar orbit, having an inclination of 86.3� (meaning it passed the equator at an angle of 86.3�). To understand the risks associated with this flight path and altitude—it had an apogee of 780km and a perigee of 774km, putting it right in a high-debris band—we need to know how much junk it is flying through. This is a serious challenge, but NASA has an Orbital Debris Engineering Model (ORDEM2000) that is free for people to download and use.

Using the ORDEM2000 model, I calculated the debris flux that the Iridium-33 satellite would have to contend with during its 2009 orbits. As you can see from bar graph, the amount of debris is considerably higher at the poles (90� and 270�) than it is in the equatorial region (0� and 180�). Integrating this flux value over the orbital path and using some published data on the LM 700 satellite—and hoping I did all of my unit/coordinate conversions correctly—produces a result that indicates, on average, the Iridium-33 satellite would be struck by an object large enough to do damage once every 44 years. (Again, assuming that the debris flux calculated by ORDEM2000 for 2009 is representative and I interpreted the results correctly.) Clearly this not a common occurrence, but also not so remote that the possibility can be ignored.

Since 1991, there have been 8 major satellite collisions, not including China's ASAT test. This would lend credence to the number I calculated: given the number of active and inactive satellites, the chance of collisions are small, but non-zero.

This collision happened to occur in a particularly bad area, as mentioned previously. The altitudes where this collision occurred are already so congested with space debris that they are referred to as supercritical. That means debris is being generated through collisions at a faster rate than atmospheric drag can remove the existing debris from orbit.

As more and more satellites are launched into orbit, the potential for debris issues is becoming widely recognized. In a press release from the Union of Concerned Scientists, issued shortly after this collision, David Wright pointed out that a number of countries have developed a set of debris mitigation guidelines that have since been adopted by the UN. One key measure was to have countries remove defunct satellites, such as Kosmos 2251, from highly polluted orbital areas. Wright also suggested that, as "space becomes more and more crowded, the international community must begin to develop and put in place measures for space traffic management, similar to what we now have with air traffic control around busy airports."

Matt Ford
Matt is a contributing writer at Ars Technica, focusing on physics, astronomy, chemistry, mathematics, and engineering. When he's not writing, he works on realtime models of large-scale engineering systems. Emailzeotherm@gmail.com//Twitter@zeotherm

Is there any way we could launch satellites that would be able to hit debris with lasers or projectiles to allow the debris to escape the earth or slow it down enough that it would fall low enough to burn up in the atmosphere? I realize that these debris pieces are tremendously fast and therefore have huge kinetic energy...just wondering.

Looks like that idea I saw on the History Channel Star Wars special of putting plasma shields around satellites is looking more important than ever. it would really suck if a key communications satellite went down.

But first we need to start a concerted international effort to try and collect the crap up there. Somehow it needs to happen before our orbit starts to look that scene from Wall-E when the ship leaves Earth. What a freaking mess!

on average, the Iridium-33 satellite would be struck by an object large enough to do damage once every 44 years

The problem is that this once/44 year collision will put even more debris into orbit, which will cause more collisions, etc in an exponential curve of growing debris.

Why don't countries like the US practice their aim with their Star Wars technology by shooting out some of this debris? Or maybe there's a way to knock a bunch of it out of orbit--maybe launch a big blob of silly putty to slow down a bunch of it, then deorbit when it gets full of holes. I don't know--we ought to do something rather than just sit idly by while the problem gets worse and worse.

But first we need to start a concerted international effort to try and collect the crap up there. Somehow it needs to happen before our orbit starts to look that scene from Wall-E when the ship leaves Earth. What a freaking mess!

I'd rather have us start by first cleaning up the SURFACE of the Earth before it starts looking like every Earthbound scene in WALL•E.

Political Correctness prevents the US from using its Star Wars technology. A system to image and destroy space debris has been conceived and offered to the government more than 10 years ago. However, anything that can remove debris would also look much like an ASAT system - hence government organizations steer away from these concepts.

The star wars system was intended to destroy satellites or missiles, not halt their motion. Shooting a satellite moving at 10 km/s with a laser results in a dead satellite moving at ~10 km/s. Even the Brilliant Pebbles concept would have had the same result: a collision between fast moving objects would result in a cloud of fast moving debris (the satellite collision here is basically the Brilliant Pebbles concept).

In fact, using a laser is about the most inefficient way to slow down debris. A 1 kg piece of debris traveling at 10 km/s (5e7 J of kinetic energy) would require over a terajoule (> 1e12 J) of laser light to bring to a stop. That assumes that the focus of your laser is good enough so that all the laser light falls on the piece of debris, which is unrealistic.

quote: But first we need to start a concerted international effort to try and collect the crap up there. Somehow it needs to happen before our orbit starts to look that scene from Wall-E when the ship leaves Earth. What a freaking mess!

I'd rather have us start by first cleaning up the SURFACE of the Earth before it starts looking like every Earthbound scene in WALL•E.

The star wars system was intended to destroy satellites or missiles, not halt their motion. Shooting a satellite moving at 10 km/s with a laser results in a dead satellite moving at ~10 km/s. Even the Brilliant Pebbles concept would have had the same result: a collision between fast moving objects would result in a cloud of fast moving debris (the satellite collision here is basically the Brilliant Pebbles concept).

The concepts I was alluding to was to vaporize small objects not bring them to a standstill. Lasers are by their nature inefficient but they could remain on the ground and hence cheap relative to launching something.

The star wars system was intended to destroy satellites or missiles, not halt their motion. Shooting a satellite moving at 10 km/s with a laser results in a dead satellite moving at ~10 km/s. Even the Brilliant Pebbles concept would have had the same result: a collision between fast moving objects would result in a cloud of fast moving debris (the satellite collision here is basically the Brilliant Pebbles concept).

The concepts I was alluding to was to vaporize small objects not bring them to a standstill. Lasers are by their nature inefficient but they could remain on the ground and hence cheap relative to launching something.

I doubt that vaporizing satellite pieces or blowing them up will work. That's really part of the problem more than the solution. Still, the idea is great for the engineering imagination.

Maybe we could snag them in lightweight high volume bags, parachutes of sorts. We could have great sport with designing them. These could multiply the drag against air molecules up there hundreds or thousands of times and drag them down, while also making them easier to see. Hunter satellites could be used to deploy these bags.

More aggressively by far, we could attempt actual catches, like with a robotic arm and a box filled with foam. The catching satellite would have to be powered, deliberately moving into position to find the satellites.

Both of these would be sport for mathematics & optimization specialists, who could use various algorithms to try to get the most junk down before the satellite runs out of energy, mushy materials, or both.

It is now a requirement that any US spacecraft launched into earth orbit must have a deorbiting capability. All US spacecraft must be deorbited at the conclusion of their useful life. There are also plans to retrofit earlier spacecraft which were launched without a deorbiting capability such Hubble with a deorbiting capability.

The last thing anyone should ever want to do to make earth orbits safe is to use lasers on a spacecraft. Light is a great carrier of energy but a very poor carrier on momentum. The energy required to change the velocity of a 1kg spacecraft by 1 m/s would light up the US for months. The result of any laser hit would be to shatter the spacecraft into hundreds of pieces insuring the collision with any manned vehicle would be deadly (as in shotgun). Better to have it whole and punch neat entrance and exit holes than to make Swiss cheese.

PS That was the conclusion from research done 25 years ago about how to handle meteors that might collide with the Shuttle or the Space Station.

Originally posted by s4b:Light is a great carrier of energy but a very poor carrier on momentum. The energy required to change the velocity of a 1kg spacecraft by 1 m/s would light up the US for months.

The US uses roughly 320 billion kilowatt hours in the form of electricity every month. If you're changing the momentum of the spacecraft (at 1kg, space debris?) using photons that are absorbed by it, then the requisite energy is:

E = pc
E = 1kg x 1m/s x 3e8m/s
E = 300MJ
E ~ 83kWh

So you're only out by a factor of 4 billion.

quote:

The result of any laser hit would be to shatter the spacecraft into hundreds of pieces insuring the collision with any manned vehicle would be deadly (as in shotgun). Better to have it whole and punch neat entrance and exit holes than to make Swiss cheese.

Probably for larger objects that are trackable the best thing would be to simply steer around them. It's not like they are moving around randomly or anything... there is nothing really to bounce them around or change their directions (if there was this would not be a problem).

If you have a few big things that are meanacing or you know are very likely to run into each other then you'll just have to figure out a way to shoot them down.

I am envisioning a foam-like substance.. something gummy with a huge potential for expanding volume but have very strong bond.

So for example if your aiming to shoot down the satellite you'd have to have a sort of 'attack' satellite that would fire a missile at the target junk satellite. You'd aim for the missile to run along a similar trajectory and just before impact it would have it's tip explode into a big greasy, sticky, foaming ball and just slam into the side of the thing. Then set off some solid fuel booster to shove the satalitte off course into a decaying orbit and have it burn up a few days or weeks later.

Imagine you standing on the sidewalk and throwing some massive way-to-much-marshmallow rice crispy ball at the head of a passing bicyclist in order to knock him down.

The foam will glue together the pieces it runs into and you design the chemistry to break down in UV light after a few days and turn into dust.

---------------------

For small projectiles the solution would be to armor the satellites.

For satellites that are likely to run into a debris field with ~1cm sized objects then you create a 'deflector shield' designed by taking layers of lightweight sticky foam in between soft-ish metal layers. You'd have to design it to try to capture and redirect the movement of objects that it runs into away from the core of the satellite while capturing as much junk as it can. For stuff it can't capture then hopefully it will deflect the item enough as it's passing through the shield so that it can avoid the most critical parts of the satellite and if your lucky it would change enough direction to help it degrade out of orbit quicker.

The idea being that you do not inject the foam into the satellite until it's ready to be in orbit. That way you minimize the volume of the object you have to lift into space.

That's the problem with trying to remember the results of a paper that I wrote 25 years ago.

In the mid 80's there was a proposal floated to divert meteors from hitting the Space Station using a radar and laser deflector (don't ask me to go into the politics of why the idea was floated). The idea was to scan the space in front of the hole the SS was boring through space, find any meteors big enough to puncture a crew module and deflect then just enough to miss the SS. I was floored when I saw it and soon realized that the idea was absurd.

The radar would have to be a very high powered phased array.

The energy required would be several seconds of the entire SS solar array output.

And the laser would shatter the meteor and not move it. The result would the that the expanding debris cloud would puncture the crew module in hundreds of places. Not good. One big hole is a lot easier to patch than a lot of small ones.

Specific heat of iron 449 j/(kg degree Kelvin). To transfer enough momentum to a 1 kg iron meteor would heat the meteorite by almost 1,000,000 degrees K. ( The meteor would have shattered long before it was vaporized ).

The flux of large meteors big enough to puncture the SS or Shuttle was also so small that it would be millions of years between strikes.

The idea was shelved.

There are thousands of micrometeor hits on every spacecraft in orbit. JSC launched a spacecraft called LDEF in the 1990s to look at space environments and it was had thousands of microscope divots.

Sometime later, I believe there was a small crack in a Shuttle window. When the impact was examined, it was found to have been caused by a small fleck of paint from .... drum roll .... another shuttle. Ever since the agency has been very aware of orbital debris and instituted the policy that all non-functioning spacecraft must be deorbited. I believe that ESA, NASDA and Russia have similar policies.(Anyone out there know for sure?)

The next Hubble servicing mission will attach a docking mechanism so that a planned robotic mission, scheduled for ~2014, can dock with Hubble and attach a deorbit mechanism.

Originally posted by slogger:I hope Planetes is the future. Being a debris hauler would be awesome.

Had you watched the special features, you'd have seen an interview with a few people at NASA who point out that debris hauling would never be remotely close to an efficient way to handle debris. I too still wish to be a debris hauler though

Sorry to threadjack, but is anybody else at all concerned that we are constantly shooting terrestrial resources - particularly metals - out into space, and not collecting it back again (in any form)? Not that I'm against progress in the area of space, but it does result in a net loss of resources for Earth, and until we figure out how to get to other planets and mine them, I worry that one day we'll run out of things to shoot into space without the ability to replenish, leaving us stranded on a barren rock.

Sorry to threadjack, but is anybody else at all concerned that we are constantly shooting terrestrial resources - particularly metals - out into space, and not collecting it back again (in any form)? Not that I'm against progress in the area of space, but it does result in a net loss of resources for Earth, and until we figure out how to get to other planets and mine them, I worry that one day we'll run out of things to shoot into space without the ability to replenish, leaving us stranded on a barren rock.

No. If we had that much launch capacity, we'd be able to get to pretty much anywhere in this solar system we'd want.

Originally posted by zzyss:Sorry to threadjack, but is anybody else at all concerned that we are constantly shooting terrestrial resources - particularly metals - out into space, and not collecting it back again (in any form)? Not that I'm against progress in the area of space, but it does result in a net loss of resources for Earth, and until we figure out how to get to other planets and mine them, I worry that one day we'll run out of things to shoot into space without the ability to replenish, leaving us stranded on a barren rock.

Probably in excess of 99% of the stuff we shoot up into space is in orbit around Earth, which means it will eventually make its way back down. Very little is sent out of Earth's gravitational well, where it is essentially lost forever.